The present invention is in the field of axle assemblies for rear suspensions of front wheel drive motor vehicles. More particularly, the invention relates to an inventive connection of a rear suspension axle assembly twist beam to a control arm and a method of manufacture thereof.
One type of axle assembly commonly used in the rear suspension of front wheel drive vehicles is commonly referred to as a trailing twist axle or simply a twist axle. Twist axles are mounted to the underside of a vehicle at a pair of bushings. The bushings are typically disposed at extreme ends of an axle arm. The axle arms are also commonly referred to as the control arms. The control arms typically extend rearward from the bushings. The bushings define an axle pivot axis about which the rear axle assembly pivots after being mounted to the vehicle. A transverse beam connects the two parallel spaced control arms.
The transverse beam is commonly referred to as a twist beam. The twist beam is resistant to bending but resilient relative to torsional stress. Many twist beams are profiled in the shape of an inverted U having first and second sides. The inverted U design raises the torsional deflection axis of the twist beam relative to a closed tube.
The control arms along their rearward ends typically have connected thereto a spring seat. The spring seat is provided on the control arm to support a suspension coil spring which is disposed between the vehicle body and the control arm. A shock absorber having one end attached to the control arm and a second end attached to the vehicle body is usually mounted near the coil spring. Depending upon the structure of the control arms, a transversely oriented track bar may or may not be placed between the control arm and the vehicle body to laterally stabilize the axle assembly. Depending on the desired torsional stiffness of the axle assembly, the axle assembly may or may not have a transversely extending stabilizer bar disposed within or in close proximity to the twist beam.
Each control arm has connected thereto a spindle mounting plate. The spindle mounting plate can be part of the spring seat or can be optionally located elsewhere, separate from the spring seat. A spindle assembly is mounted to each of the spindle mounting plates. Each spindle assembly typically includes a spindle and a unitary flange for mounting to the spindle mounting plates. The spindle is fixed relative to the spindle mounting plate. A wheel bearing is disposed over the spindle. A rotating brake element such as a brake drum or brake disk turns on a wheel bearing mounted on the spindle by way of the wheel bearing. A wheel is mounted to the rotative brake elements for unitary rotation therewith.
Typically the control arms are welded to the extreme ends of the twist beam. The weld between the twist beam and the control arm is one of, if not the, most critical welds of the axle assembly. Typically, each end of the twist beam is stamped to mate around a respective control arm on the end board surface of the control arm only. The above noted construction requires a constant fit-up and nearly perfect weld. Any weld deficiencies or fit-up gap variation can dramatically impact the fatigue life of the axle assembly. In addition, if the twist beam/control arm weld should fail, the control arm may separate from the twist beam. It is desired to provide a rear axle assembly having a twist beam and control arm connection which lowers the cost of fabrication and achieves a high strength reliable joint between the twist beam and control arm. It is further desirable to provide a method of connecting the twist beam to the control arm wherein the control arm is retained to the twist beam even if there has been a failure in a connective weld between the twist beam and control arm. It is also a desire to provide a twist beam control arm connection which is more forgiving in fit-up variation.
To satisfy the above-noted and other desires, the revelation of the present invention is brought forth. In a preferred embodiment the present invention provides a rear suspension having an axle with a generally U-shaped or V-shaped twist beam. The twist beam on its extreme ends is penetrated by the corresponding control arms. The control arms of the present invention penetrate through apertures provided into the twist beam. The first and second walls of the twist beam are brought toward one another to allow the control arm to penetrate through the respective first and second apertures provided in the walls of the twist beam. After insertion through the walls of the twist axle, the twist axle is allowed to angularly expand again to its free state wherein it locks the twist beam to the control arm. A slight weld may be added to further ensure the connection of the control arm to the twist beam.